Heat your oven to 400ºF.
Heat the olive oil in a cast iron pan set over high heat. Add the pork chops and cook 3-4 minutes per side, or until deeply browned. Transfer to the oven and roast 8-10 minutes, or until cooked through.
Remove the pan to the oven and transfer the pork chops to a plate to rest. Pour all but 1 tablespoon of fat from the pan and return it to the stove.
Add the shallot and garlic and cook over medium heat until softened, 3-4 minutes. stir in the rosemary and thyme and cook 1 minute. Add the chicken stock and bring to a rapid simmer; let reduce for 1/3.
Stir in the butter, if using. Add the grapes and cook 2-3 minutes, or until warmed through.
Serve the grapes and sauce over the pork chops.